Difference between revisions of "EXTLINUX"

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==EXTLINUX - SYSLINUX for ext2/ext3 filesystems==
+
EXTLINUX is a Syslinux variant which boots from a Linux filesystem.
EXTLINUX is a new syslinux derivative, which boots from a Linux
+
 
ext2/ext3 filesystem.
+
EXTLINUX [[Filesystem|supports]]:<br />
 +
{{V|3.00+}}ext2/3,<br />
 +
{{V|4.00+}}FAT12/16/32, ext2/3/4, Btrfs,<br />
 +
{{V|4.06+}}FAT12/16/32, NTFS, ext2/3/4, Btrfs,<br />
 +
{{V|5.01+}}FAT12/16/32, NTFS, ext2/3/4, Btrfs, XFS,<br />
 +
{{V|6.03+}}FAT12/16/32, NTFS, ext2/3/4, Btrfs, XFS, UFS/FFS,<br />
 +
 
  
 
It works the same way as SYSLINUX, with a few slight modifications.
 
It works the same way as SYSLINUX, with a few slight modifications.
  
1. The installer is run on a *mounted* filesystem.  Run the extlinux
 
  installer on the directory in which you want extlinux installed:
 
  
        extlinux /boot
+
1. The [[install]]er runs on a *'''mounted'''* filesystem.
 +
Run the extlinux installer on the directory in which you want EXTLINUX installed:
  
  NOTE: this doesn't have to be the root directory of a filesystem.
+
extlinux --install /boot  
  If /boot is a filesystem, you can do:
+
  
        mkdir -p /boot/extlinux
+
Specify <tt>--install (-i)</tt> to install for the first time, or <tt>--update (-U)</tt> to upgrade a previous installation.
        extlinux /boot/extlinux
+
  
  ... to create a subdirectory and install extlinux in it.  
+
NOTE: This does not have to be the root directory of a filesystem.
 +
If "<tt>/boot</tt>" is a mount point of a supported filesystem, then you can do:
  
 +
mkdir -p /boot/extlinux
 +
extlinux --install /boot/extlinux
  
2. The configuration file is called "extlinux.conf", and is expected
+
... to create a subdirectory and install EXTLINUX in it.  
  to be found in the same directory as extlinux is installed in.
+
  
  
3. Pathnames can be absolute or relative; if absolute (with a leading
+
2. The [[config]]uration file is called "<tt>extlinux.conf</tt>", and is expected
  slash), they are relative to the root of the filesystem on which
+
to be found in the same directory as EXTLINUX is installed in.
  extlinux is installed (/boot in the example above), if relative,
+
  they are relative to the extlinux directory.
+
  
  extlinux supports subdirectories, but the total path length is
+
Since v.4.02, <tt>syslinux.cfg</tt> and {{nowrap|<tt>[/boot/]syslinux/</tt>}} are generic terms and also valid for EXTLINUX.
  limited to 255 characters.
+
<tt>extlinux.conf</tt> and {{nowrap|<tt>[/boot/]extlinux/</tt>}} take precedence for EXTLINUX if they are present.
  
  
4. EXTLINUX now supports symbolic links.  However, extremely long
+
3. Pathnames can be absolute or relative;
  symbolic links might hit the pathname limit.  Also, please note
+
if absolute (with a leading slash),  
  that absolute symbolic links are interpreted from the root *of the
+
they are relative to the root of the filesystem on which EXTLINUX is installed (<tt>/boot</tt> in the example above);
  filesystem*, which might be different from now the running system
+
if relative,  
  would interpret it (e.g. in the case of a separate /boot
+
they are relative to the Current Working Directory -
  partition.) Therefore, use relative symbolic links if at all
+
initially the EXTLINUX directory (where <tt>extlinux.conf</tt> - or the alternative <tt>syslinux.cfg</tt> - is located).
  possible.
+
<!-- See [[Configuration_location_and_name]] -->
  
 +
EXTLINUX supports subdirectories, but the total path length is limited to 255 characters.
  
Note that EXTLINUX installs in the filesystem partition like a
 
well-behaved bootloader :)  Thus, it needs a master boot record in the
 
partition table; the mbr.bin shipped with SYSLINUX should work well.
 
To install it just do:
 
  
        cat mbr.bin > /dev/XXX
+
4. EXTLINUX supports symbolic links.
 +
However, extremely long symbolic links might hit the pathname limit.
 +
Also, please note that absolute symbolic links are interpreted from the root {{nowrap|*<u>of the filesystem</u>*}},
 +
which might be different from how the running system would interpret it (e.g. in the case of a separate <tt>/boot</tt> partition.)
 +
Therefore, use relative symbolic links if at all possible.
  
... where /dev/XXX is the appropriate master device, e.g. /dev/hda,
 
and make sure the correct partition in set active.
 
  
 +
5. EXTLINUX has "boot-once" support.
 +
The boot-once information is stored in an on-disk datastructure,
 +
part of ldlinux.sys,
 +
called the "''Auxillary Data Vector''".
 +
The Auxilliary Data Vector is also available to c32 modules that want to store small amounts of information.
  
If you have multiple disks in a software RAID configuration, the
+
To set the boot-once information:
preferred way to boot is:
+
  
* Create a separate RAID-1 partition for /boot.  Note that the Linux
+
extlinux --once 'command' /boot/extlinux
  RAID-1 driver can span as many disks as you wish.
+
  
* Install the MBR on *each disk*, and mark the RAID-1 partition
+
where "''command''" is any command you could enter at the Syslinux command line, preferably a label.
  active.
+
The boot-once information will be executed on the next boot and then erased.
  
* Run "extlinux /boot" to install extlinux.  This will install it on
+
To clear the boot-once information:
  all the drives in the RAID-1 set, which means you can boot any
+
  combination of drives in any order.
+
  
 +
extlinux --clear-once /boot/extlinux
  
 +
If EXTLINUX is used on a RAID-1, this is recommended, since under certain circumstances a RAID-1 rebuild can "resurrect" the boot-once information otherwise.
  
It is not required to re-run the extlinux installer after installing
+
To clear the entire Auxillary Data Vector:
new kernels.  If you are using ext3 journalling, however, it might be
+
desirable to do so, since running the extlinux installer will flush
+
the log.  Otherwise a dirty shutdown could cause some of the new
+
kernel image to still be in the log.  This is a general problem for
+
boot loaders on journalling filesystems; it is not specific to
+
extlinux.  The "sync" command does not flush the log on the ext3
+
filesystem.
+
  
 +
extlinux --reset-adv /boot/extlinux
  
The SYSLINUX series boot loaders support chain loading other operating
+
This will erase all data stored in the ADV, including boot-once.
systems via a separate module, chain.c32 (located in
+
com32/modules/chain.c32).  To use it, specify a LABEL in the
+
configuration file with KERNEL chain.c32 and
+
APPEND [hd|fd]<number> [<partition>]
+
  
For example:
+
The <tt>--once</tt>, <tt>--clear-once</tt>, and <tt>--reset-adv</tt> commands can be combined with {{nowrap|<tt>--install</tt>}} or {{nowrap|<tt>--update</tt>}}, if desired.
 +
The ADV is preserved across updates, unless {{nowrap|<tt>--reset-adv</tt>}} is specified.
  
# Windows CE/ME/NT, a very dense operating system.
 
# Second partition (2) on the first hard disk (hd0);
 
# Linux would *typically* call this /dev/hda2 or /dev/sda2.
 
LABEL cement
 
        KERNEL chain.c32
 
        APPEND hd0 2
 
  
See also README.menu.
+
Note that EXTLINUX installs in the filesystem partition like a well-behaved bootloader :).
 +
Thus, it needs a master boot record in the partition table;
 +
the [[Mbr|mbr.bin]] shipped with SYSLINUX should work well.
 +
To install it:
 +
 
 +
cat mbr.bin > /dev/XXX
 +
 
 +
... where ''/dev/XXX'' is the appropriate master device, e.g. /dev/hda,
 +
and make sure the correct partition is set as "active".
 +
 
 +
 
 +
If you have multiple disks in a software RAID configuration,
 +
the preferred way to boot is:
 +
 
 +
* Create a separate RAID-1 partition for /boot.
 +
:  Note that the Linux RAID-1 driver can span as many disks as you wish.
 +
 
 +
* Install the MBR on *<u>each disk</u>*, and mark the RAID-1 partition as "active".
 +
 
 +
* Run {{nowrap|"<code>extlinux --raid --install /boot</code>"}} to install EXTLINUX.
 +
:  This will install it on all the drives in the RAID-1 set, which means you can boot any combination of drives in any order.
 +
 
 +
 
 +
 
 +
It is not required to re-run the extlinux installer after installing new kernels.
 +
If you are using ext3 journalling, however, it might be desirable to do so, since running the extlinux installer will flush the log.
 +
Otherwise a dirty shutdown could cause some of the new kernel image to still be in the log.
 +
This is a general problem for boot loaders on journalling filesystems; it is not specific to EXTLINUX.
 +
The "sync" command does not flush the log on the ext3 filesystem.
 +
 
 +
 
 +
The Syslinux Project boot loaders support chain loading other operating systems via a separate module, [[Comboot/chain.c32|chain.c32]].
 +
To use it, specify a LABEL in the configuration file with KERNEL chain.c32 and APPEND [hd|fd]<number> [<partition>].
 +
 
 +
 
 +
For example:
 +
<pre>
 +
# Windows CE/ME/NT, a very dense operating system.
 +
# Second partition (2) on the first hard disk (hd0);
 +
# Linux would *typically* call this /dev/hda2 or /dev/sda2.
 +
LABEL cement
 +
  KERNEL chain.c32
 +
  APPEND hd0 2
 +
</pre>
 +
 
 +
See also [[Comboot/menu.c32]].

Latest revision as of 21:08, 31 March 2017

EXTLINUX is a Syslinux variant which boots from a Linux filesystem.

EXTLINUX supports:
[3.00+] ext2/3,
[4.00+] FAT12/16/32, ext2/3/4, Btrfs,
[4.06+] FAT12/16/32, NTFS, ext2/3/4, Btrfs,
[5.01+] FAT12/16/32, NTFS, ext2/3/4, Btrfs, XFS,
[6.03+] FAT12/16/32, NTFS, ext2/3/4, Btrfs, XFS, UFS/FFS,


It works the same way as SYSLINUX, with a few slight modifications.


1. The installer runs on a *mounted* filesystem. Run the extlinux installer on the directory in which you want EXTLINUX installed:

extlinux --install /boot 

Specify --install (-i) to install for the first time, or --update (-U) to upgrade a previous installation.

NOTE: This does not have to be the root directory of a filesystem. If "/boot" is a mount point of a supported filesystem, then you can do:

mkdir -p /boot/extlinux
extlinux --install /boot/extlinux

... to create a subdirectory and install EXTLINUX in it.


2. The configuration file is called "extlinux.conf", and is expected to be found in the same directory as EXTLINUX is installed in.

Since v.4.02, syslinux.cfg and [/boot/]syslinux/ are generic terms and also valid for EXTLINUX. extlinux.conf and [/boot/]extlinux/ take precedence for EXTLINUX if they are present.


3. Pathnames can be absolute or relative; if absolute (with a leading slash), they are relative to the root of the filesystem on which EXTLINUX is installed (/boot in the example above); if relative, they are relative to the Current Working Directory - initially the EXTLINUX directory (where extlinux.conf - or the alternative syslinux.cfg - is located).

EXTLINUX supports subdirectories, but the total path length is limited to 255 characters.


4. EXTLINUX supports symbolic links. However, extremely long symbolic links might hit the pathname limit. Also, please note that absolute symbolic links are interpreted from the root *of the filesystem*, which might be different from how the running system would interpret it (e.g. in the case of a separate /boot partition.) Therefore, use relative symbolic links if at all possible.


5. EXTLINUX has "boot-once" support. The boot-once information is stored in an on-disk datastructure, part of ldlinux.sys, called the "Auxillary Data Vector". The Auxilliary Data Vector is also available to c32 modules that want to store small amounts of information.

To set the boot-once information:

extlinux --once 'command' /boot/extlinux

where "command" is any command you could enter at the Syslinux command line, preferably a label. The boot-once information will be executed on the next boot and then erased.

To clear the boot-once information:

extlinux --clear-once /boot/extlinux

If EXTLINUX is used on a RAID-1, this is recommended, since under certain circumstances a RAID-1 rebuild can "resurrect" the boot-once information otherwise.

To clear the entire Auxillary Data Vector:

extlinux --reset-adv /boot/extlinux

This will erase all data stored in the ADV, including boot-once.

The --once, --clear-once, and --reset-adv commands can be combined with --install or --update, if desired. The ADV is preserved across updates, unless --reset-adv is specified.


Note that EXTLINUX installs in the filesystem partition like a well-behaved bootloader :). Thus, it needs a master boot record in the partition table; the mbr.bin shipped with SYSLINUX should work well. To install it:

cat mbr.bin > /dev/XXX

... where /dev/XXX is the appropriate master device, e.g. /dev/hda, and make sure the correct partition is set as "active".


If you have multiple disks in a software RAID configuration, the preferred way to boot is:

  • Create a separate RAID-1 partition for /boot.
Note that the Linux RAID-1 driver can span as many disks as you wish.
  • Install the MBR on *each disk*, and mark the RAID-1 partition as "active".
  • Run "extlinux --raid --install /boot" to install EXTLINUX.
This will install it on all the drives in the RAID-1 set, which means you can boot any combination of drives in any order.


It is not required to re-run the extlinux installer after installing new kernels. If you are using ext3 journalling, however, it might be desirable to do so, since running the extlinux installer will flush the log. Otherwise a dirty shutdown could cause some of the new kernel image to still be in the log. This is a general problem for boot loaders on journalling filesystems; it is not specific to EXTLINUX. The "sync" command does not flush the log on the ext3 filesystem.


The Syslinux Project boot loaders support chain loading other operating systems via a separate module, chain.c32. To use it, specify a LABEL in the configuration file with KERNEL chain.c32 and APPEND [hd|fd]<number> [<partition>].


For example:

 # Windows CE/ME/NT, a very dense operating system.
 # Second partition (2) on the first hard disk (hd0);
 # Linux would *typically* call this /dev/hda2 or /dev/sda2.
 LABEL cement
  KERNEL chain.c32
  APPEND hd0 2

See also Comboot/menu.c32.